1. Field of the Invention
The present invention relates to an electronic component mounting board. More particularly, the present invention relates to an electronic component mounting board that is capable of securing a sufficient contact pressure irrespective of irregularities in height of electronic components and is also capable of lowering conduction resistance and inductance, relates to a method for manufacturing the same and relates to an electronic circuit unit provided with the electronic component mounting board.
2. Description of Related Art
As conventional methods of mounting an electronic component on a circuit board with electrodes with different heights and on the like, there are disclosed: a method as described for example in Japanese Unexamined Patent Application, First Publication No. H11-214594 (hereinafter, referred to as Patent Document 1) in which a mounting board using an anisotropic conductive elastomer sheet is used; a method in which a mounting board using a conductive elastomer is used as shown for example in FIG. 26; and a method in which a mounting board using blade springs as shown for example in FIG. 27.
However, in the method using an anisotropic conductive elastomer sheet as described in Patent Document 1, conductive microparticles are dispersed in the elastomer to provide conductivity. Therefore, compared with a good conductor such as a metal, it is inevitable that the elastomer will have high contact resistance and high conduction resistance. Moreover, it is difficult to make the pitch narrow. Furthermore, high costs are required because an anisotropic conductive elastomer sheet itself is expensive.
In the mounting method as shown in FIG. 26 in which one of the conductive elastomer pillars 103 is used to electrically connect a solder bump α of an electronic component 160 with a conduction portion β of a circuit board 170, contact resistance and conduction resistance are high compared with a good conductor such as a metal, as is the case where an anisotropic conductive elastomer sheet is used. To lower the contact resistance and the conduction resistance, a proportion of the conductive microparticles mixed in the elastomer may be increased. However, this will decrease the deformability of the conductive elastomer pillars 103. That is, the conductive elastomer pillars 103 become highly elastic rigid bodies, for which it is difficult to have a displacement amount sufficient for strokes of contact electrodes. When the electronic component 160 and the circuit board 170 with irregularity in height are mounted without a sufficient stroke amount being provided like this, the conductive elastomer pillars 103 are brought into mechanical contact with tall electrodes to allow for conduction, but are brought into insufficient mechanical contact with short electrodes. As a result, there is a possibility of poor conduction or increase in contact resistance.
In the method as shown in FIG. 27 in which blade springs 113 are used to electrically connect an electronic component 160 with a circuit board 170, it is required to provide a mechanical spring structure. Therefore, it is difficult to make a terminal pitch small. In addition, there is a possibility of decrease in conductivity due to oxidation of the blade spring 113.
Furthermore, to secure a sufficient stroke amount, it is required to make the blade springs long. Moreover, to make the terminal pitch small, it is required to make the blade springs thin. Therefore, in either case, inductance is increased. As a result, it is difficult to apply this method to high frequency electronic components.